Scientific balloons may be used to elevate scientific payloads. Generally, a scientific payload may be suspended from a scientific balloon via a suspension train. Scientific instruments configured to capture data may be contained in the scientific payload. Data capture is facilitated by aiming, i.e., pointing, the scientific payload in a target direction. The target direction may include an angle in azimuth related to a defined reference direction. During suspension, the balloon may rotate. For example, the balloon may acquire angular momentum during ascent through layers of atmosphere and/or due to torque from surrounding winds at float altitude. A mechanism, e.g., a motor, may be included in and/or coupled to the scientific payload and coupled to the suspension train. The motor may then be configured to rotate the scientific payload relative to the balloon to adjust a pointing direction (i.e., pointing angle) of the scientific payload.
The suspension train is typically relatively light compared to the payload and may generally have a relatively weak effective torsional spring constant. Thus, applying a torque, e.g., by the motor, to a suspension point of the scientific payload may at least initially twist the suspension train rather than steering the payload itself. The scientific payload and suspension train typically form a torsional pendulum with a period between 20 seconds and 200 seconds and decay times of hundreds of periods. Thus, the payload pointing direction may recover relatively slowly following a disturbing torque.
The suspension train may be “stiffened” by a reaction wheel configured to serve as a source or a sink for angular momentum. Torque to rotate the payload may be supplied by a torque motor. The reaction wheel is relatively heavy and is configured to resist rotation. The motor torque configured to steer the payload may then be applied to the reaction wheel rather than the relatively light suspension train. In other words, the motor can “push against” the reaction wheel. A secondary system may be included configured to gradually “dump” angular momentum into the balloon.